Preamble formats for mimo wireless communications

ABSTRACT

A method for generating a preamble of a frame for a multiple input multiple output (MIMO) wireless communication begins by, for each transmit antenna, generating a carrier detect field. The method continues by, for a first grouping of the transmit antennas, generating a first guard interval following the carrier detect field; and generating at least one channel sounding field. Continuing, the method applies cyclical shift prior to transmission via the first grouping of the transmit antennas. When the MIMO wireless communication includes more than the first grouping of the transmit antennas, for another grouping of the transmit antennas. For the another grouping of the transmit antennas, generating at least one other channel sounding field. The method proceeds by generating the first guard interval prior to the at least one other channel sounding field, and applying another cyclical shift prior to transmission via the another grouping of the transmit antennas.

CROSS REFERENCE TO RELATED PATENTS

The present U.S. Utility patent application claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility patent application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility patent application for all purposes:

1. U.S. Utility application Ser. No. 12/173,796, entitled “PREAMBLE FORMATS FOR MIMO WIRELESS COMMUNICATIONS,” (Attorney Docket No. BP3972C1), filed Jul. 15, 2008, pending, which claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes:

2. U.S. Utility application Ser. No. 10/973,595, entitled “PREAMBLE FORMATS FOR MIMO WIRELESS COMMUNICATIONS,” (Attorney Docket No. BP3972), filed Oct. 26, 2004, now issued as U.S. Pat. No. 7,423,989, on Sep. 9, 2008, which claims priority pursuant to 35 U.S.C. §119(e) to the following U.S. Provisional Patent Applications which are hereby incorporated herein by reference in their entirety and made part of the present U.S. Utility Patent Application for all purposes:

-   -   a. U.S. Provisional Application Ser. No. 60/544,605, entitled         “MULTIPLE PROTOCOL WIRELESS COMMUNICATIONS IN A WLAN,” (Attorney         Docket No. BP3515), filed Feb. 13, 2004, expired;     -   b. U.S. Provisional Application Ser. No. 60/545,854, entitled         “WLAN TRANSMITTER HAVING HIGH DATA THROUGHPUT,” (Attorney Docket         No. BP3516), filed Feb. 19, 2004, expired;     -   c. U.S. Provisional Application Ser. No. 60/568,914, entitled         “MIMO PROTOCOL FOR WIRELESS COMMUNICATIONS,” (Attorney Docket         No. BP3515.1), filed May 7, 2004, expired; and     -   U.S. Provisional Application Ser. No. 60/573/782, entitled         “PREAMBLE FORMATS FOR MIMO WIRELESS COMMUNICATIONS,” (Attorney         Docket No. BP3515.2), filed May 24, 2004, expired.

TECHNICAL FIELD

The invention relates generally to wireless communication systems and more particularly to supporting multiple wireless communication protocols within a wireless local area network.

DESCRIPTION OF RELATED ART

Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.

Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.

For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.

As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.

As is further known, the standard to which a wireless communication device is compliant within a wireless communication system may vary. For instance, as the IEEE 802.11 specification has evolved from IEEE 802.11 to IEEE 802.11b to IEEE 802.11a and to IEEE 802.11g, wireless communication devices that are compliant with IEEE 802.11b may exist in the same wireless local area network (WLAN) as IEEE 802.11g compliant wireless communication devices. As another example, IEEE 802.11a compliant wireless communication devices may reside in the same WLAN as IEEE 802.11g compliant wireless communication devices. When legacy devices (i.e., those compliant with an earlier version of a standard) reside in the same WLAN as devices compliant with later versions of the standard, a mechanism is employed to insure that legacy devices know when the newer version devices are utilizing the wireless channel as to avoid a collision.

For instance, backward compatibility with legacy devices has been enabled exclusively at either the physical (PHY) layer (in the case of IEEE 802.11b) or the Media-Specific Access Control (MAC) layer (in the case of IEEE 802.11g). At the PHY layer, backward compatibility is achieved by re-using the PHY preamble from a previous standard. In this instance, legacy devices will decode the preamble portion of all signals, which provides sufficient information for determining that the wireless channel is in use for a specific period of time, thereby avoid collisions even though the legacy devices cannot fully demodulate and/or decode the transmitted frame(s).

At the MAC layer, backward compatibility with legacy devices is enabled by forcing devices that are compliant with a newer version of the standard to transmit special frames using modes or data rates that are employed by legacy devices. For example, the newer devices may transmit Clear to Send/Ready to Send (CTS/RTS) exchange frames and/or CTS to self frames as are employed in IEEE 802.11g. These special frames contain information that sets the NAV (network allocation vector) of legacy devices such that these devices know when the wireless channel is in use by newer stations.

Both of the existing mechanisms for backward compatibility suffer from a performance loss relative to that which can be achieved without backward compatibility and are used independently of each other.

Therefore, a need exists for a method and apparatus that enables multiple protocols to be supported within a wireless communication system, including wireless local area networks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a wireless communication system in accordance with the present invention;

FIG. 2 is a schematic block diagram of a wireless communication device in accordance with the present invention;

FIG. 3 is a schematic block diagram of another wireless communication device in accordance with the present invention;

FIG. 4 is a schematic block diagram of an RF transmitter in accordance with the present invention;

FIG. 5 is a schematic block diagram of an RF receiver in accordance with the present invention;

FIG. 6 is a schematic block diagram of an access point communicating with wireless communication devices in accordance with the present invention;

FIG. 7 is a diagram depicting one type of wireless communication in accordance with the present invention;

FIG. 8 is a diagram depicting one type of MIMO wireless communication in accordance with the present invention;

FIG. 9 is a diagram of a preamble of frame using cyclic shifting for two transmit antennas in accordance with the present invention;

FIG. 10 is a diagram of a preamble of frame using sparse symbols and/or tones for two transmit antennas in accordance with the present invention;

FIG. 11 is a diagram of a preamble of frame using cyclic shifting for three transmit antennas in accordance with the present invention;

FIG. 12 is another diagram of a preamble of frame using cyclic shifting for three transmit antennas in accordance with the present invention;

FIG. 13 is a diagram of a preamble of frame using sparse symbols and/or tones for three transmit antennas in accordance with the present invention;

FIG. 14 is a diagram of a preamble of frame using cyclic shifting for four transmit antennas in accordance with the present invention;

FIG. 15 is another diagram of a preamble of frame using cyclic shifting for four transmit antennas in accordance with the present invention;

FIG. 16 is a diagram of a preamble of frame using sparse symbols and/or tones for four transmit antennas in accordance with the present invention;

FIG. 17 is a diagram depicting another type of wireless communication in accordance with the present invention;

FIG. 18 is a diagram depicting another type of MIMO wireless communication in accordance with the present invention;

FIG. 19 is a diagram of a preamble of frame using cyclic shifting for two transmit antennas using a legacy portion in accordance with the present invention;

FIG. 20 is a diagram of a preamble of frame using cyclic shifting for three transmit antennas using a legacy portion in accordance with the present invention;

FIG. 21 is a diagram of a preamble of frame using cyclic shifting for four transmit antennas using a legacy portion in accordance with the present invention;

FIG. 22 is a diagram of yet another wireless communication in accordance with the present invention;

FIG. 23 is a diagram of yet another MIMO wireless communication in accordance with the present invention;

FIG. 24 is a logic diagram of a method for multiple protocol communications in accordance with the present invention;

FIG. 25 is a logic diagram of a method for monitoring success of wireless multiple protocol communications in accordance with the present invention;

FIG. 26 is a logic diagram of a method for a wireless communication device to participate in a multiple protocol communication in accordance with the present invention;

FIG. 27 is a logic diagram of another method for a wireless communication device to participate in a multiple protocol communication in accordance with the present invention;

FIG. 28 is a logic diagram of yet another method for a wireless communication device to participate in a multiple protocol communication in accordance with the present invention;

FIG. 29 is a diagram of simultaneous second channel sounding in accordance with the present invention;

FIG. 30 is another diagram of simultaneous second channel sounding in accordance with the present invention;

FIG. 31 is yet another diagram of simultaneous second channel sounding in accordance with the present invention; and

FIG. 32 is a further diagram of simultaneous second channel sounding in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Provided are preamble formats for MIMO wireless communications. In one embodiment, a method for generating a preamble of a frame for a Multiple Input Multiple Output (MIMO) wireless communication begins by, for each transmit antenna of the MIMO wireless communication, generating a carrier detect field. The method continues by, for a first grouping of the transmit antennas of the MIMO wireless communication: generating a first guard interval following the carrier detect field; and generating at least one channel sounding field, wherein, from transmit antenna to transmit antenna in the first grouping, and wherein the at least one channel sounding field follows the first guard interval, and applying a cyclic shift prior to transmission. The method continues by, when the MIMO wireless communication includes more than the first grouping of the transmit antennas, for another grouping of the transmit antennas: generating at least one other channel sounding field, wherein, from transmit antenna to transmit antenna in the another grouping, and wherein the at least one other channel sounding field follows the at least one channel sounding field; and generating the first guard interval prior to the at least one other channel sounding field, and applying another cyclic shift prior to transmission for the another grouping of transmit antennas.

FIG. 1 is a schematic block diagram illustrating a communication system 10 that includes a plurality of base stations and/or access points 12-16, a plurality of wireless communication devices 18-32 and a network hardware component 34. The wireless communication devices 18-32 may be laptop host computers 18 and 26, personal digital assistant hosts 20 and 30, personal computer hosts 24 and 32 and/or cellular telephone hosts 22 and 28. The details of the wireless communication devices will be described in greater detail with reference to FIGS. 2 and/or 3.

The base stations or access points 12-16 are operably coupled to the network hardware 34 via local area network connections 36, 38 and 40. The network hardware 34, which may be a router, switch, bridge, modem, system controller, et cetera provides a wide area network connection 42 for the communication system 10. Each of the base stations or access points 12-16 has an associated antenna or antenna array to communicate with the wireless communication devices in its regional area, which is generally referred to as a basic service set (BSS) 9, 11, 13. Typically, the wireless communication devices register with a particular base station or access point 12-14 to receive services from the communication system 10. For direct connections (i.e., point-to-point communications), wireless communication devices communicate directly via an allocated channel to produce an ad-hoc network.

Typically, base stations are used for cellular telephone systems and like-type systems, while access points are used for in-home or in-building wireless networks. Regardless of the particular type of communication system, each wireless communication device includes a built-in radio and/or is coupled to a radio. The radio includes a highly linear amplifier and/or programmable multi-stage amplifier as disclosed herein to enhance performance, reduce costs, reduce size, and/or enhance broadband applications.

FIG. 2 is a schematic block diagram illustrating a wireless communication device that includes the host device 18-32 and an associated radio 60. For cellular telephone hosts, the radio 60 is a built-in component. For personal digital assistants hosts, laptop hosts, and/or personal computer hosts, the radio 60 may be built-in or an externally coupled component.

As illustrated, the host device 18-32 includes a processing module 50, memory 52, radio interface 54, input interface 58 and output interface 56. The processing module 50 and memory 52 execute the corresponding instructions that are typically done by the host device. For example, for a cellular telephone host device, the processing module 50 performs the corresponding communication functions in accordance with a particular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to the radio 60. For data received from the radio 60 (e.g., inbound data), the radio interface 54 provides the data to the processing module 50 for further processing and/or routing to the output interface 56. The output interface 56 provides connectivity to an output display device such as a display, monitor, speakers, et cetera such that the received data may be displayed. The radio interface 54 also provides data from the processing module 50 to the radio 60. The processing module 50 may receive the outbound data from an input device such as a keyboard, keypad, microphone, et cetera via the input interface 58 or generate the data itself. For data received via the input interface 58, the processing module 50 may perform a corresponding host function on the data and/or route it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, digital receiver processing module 64, memory 75, a digital transmitter processing module 76, and a radio transceiver. The radio transceiver includes an analog-to-digital converter 66, a filtering/gain module 68, an IF mixing down conversion stage 70, a receiver filter 71, a low noise amplifier 72, a transmitter/receiver switch 73, a local oscillation module 74, a digital-to-analog converter 78, a filtering/gain module 80, an IF mixing up conversion stage 82, a power amplifier 84, a transmitter filter module 85, and an antenna 86. The antenna 86 may be a single antenna that is shared by the transmit and receive paths as regulated by the Tx/Rx switch 73, or may include separate antennas for the transmit path and receive path. The antenna implementation will depend on the particular standard to which the wireless communication device is compliant.

The digital receiver processing module 64 and the digital transmitter processing module 76, in combination with operational instructions stored in memory 75, execute digital receiver functions and digital transmitter functions, respectively, in accordance with one or more wireless communication standards and as further function to implement one or more aspects of the functionality described with reference to FIGS. 3-11. The digital receiver functions include, but are not limited to, digital intermediate frequency to baseband conversion, demodulation, constellation demapping, decoding, and/or descrambling. The digital transmitter functions include, but are not limited to, scrambling, encoding, constellation mapping, modulation, and/or digital baseband to IF conversion. The digital receiver and transmitter processing modules 64 and 76 may be implemented using a shared processing device, individual processing devices, or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory 75 may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the processing module 64 and/or 76 implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 94 from the host device via the host interface 62. The host interface 62 routes the outbound data 94 to the digital transmitter processing module 76, which processes the outbound data 94 in accordance with a particular wireless communication standard (e.g., IEEE 802.11 and versions thereof, Bluetooth and versions thereof, et cetera) to produce digital transmission formatted data 96. The digital transmission formatted data 96 will be a digital base-band signal or a digital low IF signal, where the low IF typically will be in the frequency range of one hundred kilohertz to a few megahertz.

The digital-to-analog converter 78 converts the digital transmission formatted data 96 from the digital domain to the analog domain. The filtering/gain module 80 filters and/or adjusts the gain of the analog signal prior to providing it to the IF mixing stage 82. The IF mixing stage 82 converts the analog baseband or low IF signal into an RF signal based on a transmitter local oscillation 83 provided by local oscillation module 74. The power amplifier 84 amplifies the RF signal to produce outbound RF signal 98, which is filtered by the transmitter filter module 85. The antenna 86 transmits the outbound RF signal 98 to a targeted device such as a base station, an access point and/or another wireless communication device.

The radio 60 also receives an inbound RF signal 88 via the antenna 86, which was transmitted by a base station, an access point, or another wireless communication device. The antenna 86 provides the inbound RF signal 88 to the receiver filter module 71 via the Tx/Rx switch 73, where the Rx filter 71 bandpass filters the inbound RF signal 88. The Rx filter 71 provides the filtered RF signal to low noise amplifier 72, which amplifies the signal 88 to produce an amplified inbound RF signal. The low noise amplifier 72 provides the amplified inbound RF signal to the IF mixing module 70, which directly converts the amplified inbound RF signal into an inbound low IF signal or baseband signal based on a receiver local oscillation 81 provided by local oscillation module 74. The down conversion module 70 provides the inbound low IF signal or baseband signal to the filtering/gain module 68. The filtering/gain module 68 filters and/or gains the inbound low IF signal or the inbound baseband signal to produce a filtered inbound signal.

The analog-to-digital converter 66 converts the filtered inbound signal from the analog domain to the digital domain to produce digital reception formatted data 90. The digital receiver processing module 64 decodes, descrambles, demaps, and/or demodulates the digital reception formatted data 90 to recapture inbound data 92 in accordance with the particular wireless communication standard being implemented by radio 60. The host interface 62 provides the recaptured inbound data 92 to the host device 18-32 via the radio interface 54.

As one of average skill in the art will appreciate, the wireless communication device of FIG. 2 may be implemented using one or more integrated circuits. For example, the host device may be implemented on one integrated circuit, the digital receiver processing module 64, the digital transmitter processing module 76 and memory 75 may be implemented on a second integrated circuit, and the remaining components of the radio 60, less the antenna 86, may be implemented on a third integrated circuit. As an alternate example, the radio 60 may be implemented on a single integrated circuit. As yet another example, the processing module 50 of the host device and the digital receiver and transmitter processing modules 64 and 76 may be a common processing device implemented on a single integrated circuit. Further, the memory 52 and memory 75 may be implemented on a single integrated circuit and/or on the same integrated circuit as the common processing modules of processing module 50 and the digital receiver and transmitter processing module 64 and 76.

FIG. 3 is a schematic block diagram illustrating a wireless communication device that includes the host device 18-32 and an associated radio 60. For cellular telephone hosts, the radio 60 is a built-in component. For personal digital assistants hosts, laptop hosts, and/or personal computer hosts, the radio 60 may be built-in or an externally coupled component.

Radio 60 includes a host interface 62, a baseband processing module 63, memory 65, a plurality of radio frequency (RF) transmitters 67, 69, 71, a transmit/receive (T/R) module 73, a plurality of antennas 81, 83, 85, a plurality of RF receivers 75, 77, 79, and a local oscillation module 99. The baseband processing module 63, in combination with operational instructions stored in memory 65, execute digital receiver functions and digital transmitter functions, respectively. The digital receiver functions include, but are not limited to, digital intermediate frequency to baseband conversion, demodulation, constellation demapping, decoding, de-interleaving, fast Fourier transform, cyclic prefix removal, space and time decoding, and/or descrambling. The digital transmitter functions include, but are not limited to, scrambling, encoding, interleaving, constellation mapping, modulation, inverse fast Fourier transform, cyclic prefix addition, space and time encoding, and/or digital baseband to IF conversion. The baseband processing modules 63 may be implemented using one or more processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory 66 may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the processing module 63 implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 87 from the host device via the host interface 62. The baseband processing module 63 receives the outbound data 87 and, based on a mode selection signal 101, produces one or more outbound symbol streams 89. The mode selection signal 101 will indicate a particular mode as are indicated in mode selection tables. For example, the mode selection signal 101, with reference to Table 1 may indicate a frequency band of 2.4 GHz, a channel bandwidth of 20 or 22 MHz and a maximum bit rate of 54 megabits-per-second. In this general category, the mode selection signal will further indicate a particular rate ranging from 1 megabit-per-second to 54 megabits-per-second. In addition, the mode selection signal will indicate a particular type of modulation, which includes, but is not limited to, Barker Code Modulation, BPSK, QPSK, CCK, 16 QAM and/or 64 QAM. As is further illustrated in Table 1, a code rate is supplied as well as number of coded bits per subcarrier (NBPSC), coded bits per OFDM symbol (NCBPS), data bits per OFDM symbol (NDBPS), error vector magnitude in decibels (EVM), sensitivity which indicates the maximum receive power required to obtain a target packet error rate (e.g., 10% for IEEE 802.11a), adjacent channel rejection (ACR), and an alternate adjacent channel rejection (AACR).

The mode selection signal may also indicate a particular channelization for the corresponding mode which for the information in Table 1 is illustrated in Table 2. As shown, Table 2 includes a channel number and corresponding center frequency. The mode select signal may further indicate a power spectral density mask value which for Table 1 is illustrated in Table 3. The mode select signal may alternatively indicate rates within Table 4 that has a 5 GHz frequency band, 20 MHz channel bandwidth and a maximum bit rate of 54 megabits-per-second. If this is the particular mode select, the channelization is illustrated in Table 5. As a further alternative, the mode select signal 102 may indicate a 2.4 GHz frequency band, 20 MHz channels and a maximum bit rate of 192 megabits-per-second as illustrated in Table 6. In Table 6, a number of antennas may be utilized to achieve the higher bandwidths. In this instance, the mode select would further indicate the number of antennas to be utilized. Table 7 illustrates the channelization for the set-up of Table 6. Table 8 illustrates yet another mode option where the frequency band is 2.4 GHz, the channel bandwidth is 20 MHz and the maximum bit rate is 192 megabits-per-second. The corresponding Table 8 includes various bit rates ranging from 12 megabits-per-second to 216 megabits-per-second utilizing 2-4 antennas and a spatial time encoding rate as indicated. Table 9 illustrates the channelization for Table 8. The mode select signal 102 may further indicate a particular operating mode as illustrated in Table 10, which corresponds to a 5 GHz frequency band having 40 MHz frequency band having 40 MHz channels and a maximum bit rate of 486 megabits-per-second. As shown in Table 10, the bit rate may range from 13.5 megabits-per-second to 486 megabits-per-second utilizing 1-4 antennas and a corresponding spatial time code rate. Table 10 further illustrates a particular modulation scheme code rate and NBPSC values. Table 11 provides the power spectral density mask for Table 10 and Table 12 provides the channelization for Table 10.

The baseband processing module 63, based on the mode selection signal 101 produces the one or more outbound symbol streams 89 from the output data 88. For example, if the mode selection signal 101 indicates that a single transmit antenna is being utilized for the particular mode that has been selected, the baseband processing module 63 will produce a single outbound symbol stream 89. Alternatively, if the mode select signal indicates 2, 3 or 4 antennas, the baseband processing module 63 will produce 2, 3 or 4 outbound symbol streams 89 corresponding to the number of antennas from the output data 88.

Depending on the number of outbound streams 89 produced by the baseband module 63, a corresponding number of the RF transmitters 67, 69, 71 will be enabled to convert the outbound symbol streams 89 into outbound RF signals 91. The implementation of the RF transmitters 67, 69, 71 will be further described with reference to FIG. 4. The transmit/receive module 73 receives the outbound RF signals 91 and provides each outbound RF signal to a corresponding antenna 81, 83, 85.

When the radio 60 is in the receive mode, the transmit/receive module 73 receives one or more inbound RF signals via the antennas 81, 83, 85. The T/R module 73 provides the inbound RF signals 93 to one or more RF receivers 75, 77, 79. The RF receiver 75, 77, 79, which will be described in greater detail with reference to FIG. 4, converts the inbound RF signals 93 into a corresponding number of inbound symbol streams 96. The number of inbound symbol streams 95 will correspond to the particular mode in which the data was received (recall that the mode may be any one of the modes illustrated in Tables 1-12). The baseband processing module 63 receives the inbound symbol streams 89 and converts them into inbound data 97, which is provided to the host device 18-32 via the host interface 62.

As one of average skill in the art will appreciate, the wireless communication device of FIG. 3 may be implemented using one or more integrated circuits. For example, the host device may be implemented on one integrated circuit, the baseband processing module 63 and memory 65 may be implemented on a second integrated circuit, and the remaining components of the radio 60, less the antennas 81, 83, 85, may be implemented on a third integrated circuit. As an alternate example, the radio 60 may be implemented on a single integrated circuit. As yet another example, the processing module 50 of the host device and the baseband processing module 63 may be a common processing device implemented on a single integrated circuit. Further, the memory 52 and memory 65 may be implemented on a single integrated circuit and/or on the same integrated circuit as the common processing modules of processing module 50 and the baseband processing module 63.

FIG. 4 is a schematic block diagram of an embodiment of an RF transmitter 67, 69, 71. The RF transmitter includes a digital filter and up-sampling module 475, a digital-to-analog conversion module 477, an analog filter 479, and up-conversion module 81, a power amplifier 483 and a RF filter 485. The digital filter and up-sampling module 475 receives one of the outbound symbol streams 89 and digitally filters it and then up-samples the rate of the symbol streams to a desired rate to produce the filtered symbol streams 487. The digital-to-analog conversion module 477 converts the filtered symbols 487 into analog signals 489. The analog signals may include an in-phase component and a quadrature component.

The analog filter 479 filters the analog signals 489 to produce filtered analog signals 491. The up-conversion module 481, which may include a pair of mixers and a filter, mixes the filtered analog signals 491 with a local oscillation 493, which is produced by local oscillation module 99, to produce high frequency signals 495. The frequency of the high frequency signals 495 corresponds to the frequency of the RF signals 492.

The power amplifier 483 amplifies the high frequency signals 495 to produce amplified high frequency signals 497. The RF filter 485, which may be a high frequency band-pass filter, filters the amplified high frequency signals 497 to produce the desired output RF signals 91.

As one of average skill in the art will appreciate, each of the radio frequency transmitters 67, 69, 71 will include a similar architecture as illustrated in FIG. 4 and further include a shut-down mechanism such that when the particular radio frequency transmitter is not required, it is disabled in such a manner that it does not produce interfering signals and/or noise.

FIG. 5 is a schematic block diagram of each of the RF receivers 75, 77, 79. In this embodiment, each of the RF receivers includes an RF filter 501, a low noise amplifier (LNA) 503, a programmable gain amplifier (PGA) 505, a down-conversion module 507, an analog filter 509, an analog-to-digital conversion module 511 and a digital filter and down-sampling module 513. The RF filter 501, which may be a high frequency band-pass filter, receives the inbound RF signals 93 and filters them to produce filtered inbound RF signals. The low noise amplifier 503 amplifies the filtered inbound RF signals 93 based on a gain setting and provides the amplified signals to the programmable gain amplifier 505. The programmable gain amplifier further amplifies the inbound RF signals 93 before providing them to the down-conversion module 507.

The down-conversion module 507 includes a pair of mixers, a summation module, and a filter to mix the inbound RF signals with a local oscillation (LO) that is provided by the local oscillation module to produce analog baseband signals. The analog filter 509 filters the analog baseband signals and provides them to the analog-to-digital conversion module 511 which converts them into a digital signal. The digital filter and down-sampling module 513 filters the digital signals and then adjusts the sampling rate to produce the inbound symbol stream 95.

FIG. 6 is a schematic block diagram of an access point 12-16 communicating with wireless communication devices 25, 27 and/or 29. The wireless communication devices 25, 27 and/or 29 may be any one of the devices 18-32 illustrated in FIGS. 1-3. In this illustration, access point 12-16 includes a processing module 15, memory 17 and a radio transceiver 19. The radio transceiver 19 may be similar to the radio transceiver of each wireless communication device in architecture and may include a plurality of antennas, transmit paths and receive paths for multiple wireless communications within a proximal region or basic service set. The processing module 15 may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory 17 may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that when the processing module 15 implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. The memory 17 stores, and the processing module 15 executes, operational instructions corresponding to at least some of the steps and/or functions illustrated in FIGS. 7-32.

In this illustration, each of the wireless communication devices 25, 27 and 29 utilize a different wireless communication protocol. As illustrated, wireless communication device 25 utilizes protocol A 35, wireless communication device 27 utilizes protocol B 37 and wireless communication device 29 utilizes protocol C 39. For example, protocols A, B and C may correspond to different versions of the IEEE 802.11 standard. In particular, protocol A may correspond to IEEE 802.11b, protocol B may correspond to IEEE 802.11g and protocol C may correspond to IEEE 802.11n.

The protocols may be ordered in accordance with a protocol ordering table that has protocol A, protocol B and protocol C listed in order. The ordering may be based on the legacy of each of the corresponding protocols where the first protocol in the ordering is the oldest standard and the last entry in the protocol ordering is the most current standard. For example, in this present illustration protocol A may correspond to IEEE 802.11b, protocol B may correspond to IEEE 802.11g and protocol C may correspond to IEEE 802.11n. Alternatively, the protocol ordering may be based on a user defined and/or system administrator defined procedure. For instance, if an unacceptable number of transmission errors occur due to non-recognition of frames while utilizing protocol A to set-up wireless communications, the user may select the protocol B format for setting up a wireless communication. This concept will be described in greater detail with reference to the remaining figures.

In operation, the access point 12-16, and/or each of the wireless communication devices 25, 27 and 29, determine the protocol utilized by each of the wireless communication devices within the proximal region. Recall that the proximal region may include a basic service set and/or neighboring basic service sets and/or a direct, or ad-hoc network wherein the wireless communication devices communicate directly. Once the protocol of each of the wireless communication devices has been determined, the access point 12-16 and/or the wireless communication devices 25-29 determine, based on the protocol ordering, which protocol will be utilized to set-up a wireless communication. For instance, if protocol A corresponds to IEEE 802.11b, the communication devices will utilize a MAC level protection mechanism to set-up a wireless communication, as will be further described with reference to FIG. 22. As such, each of the wireless communication devices will utilize protocol A to set-up, or establish, a wireless communication such that the legacy devices recognize that a wireless communication is being set-up and also recognizes the duration of that wireless communication such that it will not transmit during that time, thus avoiding a collision.

Once the wireless communication is established, or set-up, utilizing a selected protocol (e.g., protocol A) from the protocol ordering, the communication device then utilizes its protocol to transmit the data for the remainder of the wireless communication. For example, wireless communication device 25 will utilize protocol A to establish and to transmit data for a wireless communication. Wireless communication device 27 will utilize protocol A to set-up a wireless communication and then use protocol B for the corresponding data transmission of the wireless communication. Similarly, wireless communication device 29 will utilize protocol A to establish, or set-up, the wireless communication and then use protocol C for the data transmission portion of the wireless communication.

As one of average skill in the art will appreciate, if the proximal region only includes wireless communication devices that utilize the same protocol, the set-up and data transmission is done using that protocol. As one of average skill in the art will further appreciate, if only two different protocols are present within the proximal region, the legacy protocol will be selected as the set-up protocol.

FIG. 7 is a diagram depicting a wireless communication between two wireless communication devices 100 and 102 that are in a proximal region where the only protocol that is used is IEEE 802.11n. The wireless communication may be direct (i.e., from wireless communication device to wireless communication device), or indirect (i.e., from a wireless communication device to an access point to a wireless communication device). In this example, wireless communication device 100 is providing frame 104 to wireless communication device 102. The frame 104 includes a wireless communication set-up information field 106 and a data portion 108. The wireless communication set-up information portion 106 includes a short training sequence 157 that may be 8 microseconds long, a 1^(st) supplemental long training sequence 159 that may be 4 microseconds long, which is one of a plurality of supplemental long training sequences 161, and a signal field 163 that may be 4 microseconds long. Note that the number of supplemental long training sequences 159, 161 will correspond to the number of transmit antennas being utilized for multiple input multiple output radio communications.

The data portion of the frame 104 includes a plurality of data symbols 165, 167, 169 each being 4 microseconds in duration. The last data symbol 169 also includes a tail bits and padding bits as needed.

FIG. 8 is a diagram depicting a wireless communication between two wireless communication devices 100 and 102 that are in a proximal region where the only protocol that is used is IEEE 802.11n. The wireless communication may be direct (i.e., from wireless communication device to wireless communication device), or indirect (i.e., from a wireless communication device to an access point to a wireless communication device). In this example, wireless communication device 100 is providing multiple frames 104-1, 104-2, 104-N to wireless communication device 102 using multiple antennas #1-#N. Each of the frames 104-1, 104-2, 104-N includes a wireless communication set-up information field 106 and a data portion 108. The wireless communication set-up information portion 106 includes a short training sequence 157 that may be 8 microseconds long, a 1^(st) supplemental long training sequence 159 that may be 4 microseconds long, which is one of a plurality of supplemental long training sequences 161, and a signal field 163 that may be 4 microseconds long. Note that the number of supplemental long training sequences will correspond to the number of transmit antennas being utilized for multiple input multiple output radio communications.

The data portion of the frame 104 includes a plurality of data symbols 165, 167, 169 each being 4 microseconds in duration. The last data symbol 169 also includes a tail bits and padding bits as needed.

In this instance, the preamble (sometimes referred to as “Greenfield”) is for the case when only 0.11n devices are present. Alternatively, it may be used with legacy devices (0.11, 0.11a, 0.11b, and 0.11g) when MAC level protection (RTS/CTS or CTS to self) is employed. (MAC level protection may also be used when legacy stations are not present to protect very long bursts.)

The short training sequence 157 maybe the same as IEEE 802.11a for TX antenna 1. For antennas 2 to N, it is a cyclic shifted version of the same sequence. In the preferred mode, the amount of cyclic shift per antenna is computed from (Antenna number−1)*800/N in nanoseconds. That is for 1 antenna the shift is zero. For 2 antennas, the shift is 0 ns for antenna 1 and 400 ns. For 3 antennas, the shifts are 0, 250, and 500 ns. For 4 antennas, the shifts are 0, 200, 400, and 600 ns. The implementation is most straightforward when the shifts are rounded to units of 50 ns (the inverse of the symbol clock frequency). Shifts may be implemented in either a forward or backward direction.

There are several possible implementations of the supplemental long training sequences 159, 161: (m=1). For this case, there will only be one long training sequence 159. For antenna 1, it will be the same as the IEEE 802.11a long training sequence 159 but only 4 microseconds long, including a 0.8 microsecond guard interval. For antennas 2 to N it is a cyclic shifted version of the same sequence. In the preferred mode, the amount of cyclic shift per antenna is computed from (Antenna number−1)*4/N in microseconds. That is for 1 antenna the shift is zero. For 2 antennas, the shift is 0 ns for antenna 1 and 4 microseconds. For 3 antennas, the shifts are 0, 2.65 microseconds, 5.35 microseconds. For 4 antennas, the shifts are 0, 2, 4, and 6 microseconds. Once again, the implementation is most straightforward when the shifts are rounded to units of 50 nanoseconds (the inverse of the symbol clock frequency). Shifts may be implemented in either a forward or backward direction.

For (m=N), the number of training sequences is equal to the number of transmit antennas. This is preferable to the (m=1) case because it will lead to less channel estimation error at the receiver, especially for large numbers of antennas. Thus, it is scalable. There are two possible choices of training sequence:

-   -   Zero space—In this case, sequences (1,1), (2,2), (3,3), . . . up         to (N,N) are the same as the IEEE 802.11a long training         sequence. All others (i.e. (1,2), (2,1), etc) are null—nothing         is transmitted during that time slot.)     -   Subchannel null—In this case, the set of sub-channels in the         training sequences is sub-divided by the number of transmit         antennas. Individual subsets are activated on each sub-training         interval.

Orthogonal sequences that are generated by multiplying the subcarriers of the IEEE 802.11a long training sequence by an m×m orthonormal matrix, such as the matrix, which generates a discrete Fourier transform.

FIG. 9 is a diagram of a preamble of a frame 104-1, 104-2 using cyclic shifting for two transmit antennas, where the communication devices are in a proximal area that only includes IEEE 802.11n compliant devices. The preamble is part of the wireless communication set up information 106 and includes a short training sequence (STS) 157, a long training sequence (LTS) 159 and 161, a signal field (SIG 1) 224, and a data field or another signal field 228. For the first antenna frame 104-1, the STS 157 is divided into two sets of symbols 232, 234. In one embodiment, the STS 157 includes 10 symbols of 800 nanoseconds as per previous versions of the IEEE 802.11x specification. The LTS 159 and 161 of the first antenna frame 104-1 includes a double guard interval (GI2) 236 that may be 1600 nanoseconds in duration and corresponds to the last 1600 nanoseconds of the LTS 159 and 161 prepended to the LTS 159 and 161.

The LTS 159 and 161 of the first antenna frame 104-1 includes a twice repeating long training sequence that may correspond to previous versions of the IEEE 802.11x specification and, wherein, tones of the LTS are divided into two sets 238, 240. The signal field 224 and the optional second signal field 228 contain information as previously discussed, which may be separated by guard intervals (GI) 220, 226.

The preamble 104-2 for the second antenna includes similar components to the preamble of the first antenna, but with the STS 157 and/or LTS 159 and 161 being cyclic shifted. As shown, the second set of symbols 234 precedes, in time, the first set of symbols 232 in the STS 157, which is the opposite of the timing sequence of the preamble for antenna 1. As is further shown, the STS 157 may include 10 symbols divided into two sets, where the first set 232 includes symbols 0-5 and the second set 234 includes symbols 6-9. For the first antenna, the first set of the symbols 232 precedes, in time, the second set 234, and for the second antenna the second set 234 precedes, in time, the first set 232. In one embodiment, the cyclic shift may be 400-1600 nanoseconds.

Each LTS pattern of the LTS field 159 and 161 may be divided into two sets 238, 240 as shown, where the first set of tones 238 precedes, in time, the second set of tones 240 for the first antenna frame 104-1 and, for the second antenna frame 104-2, the second set 240 precedes, in time, the first set 238. As such, the LTS 159 and 161 of the second antenna frame 104-2 is a cyclic shifted representation of the LTS 159 and 161 of the first antenna frame 104-1.

FIG. 10 is a diagram of a preamble of frames 104-1, 104-2 using a different form of cyclic shifting by using sparse symbols and/or tones for two transmit antennas, where the communication devices are in a proximal area that only includes IEEE 802.11n compliant devices. The preamble is part of the wireless communication set up information 106 and includes a short training sequence (STS) 157, a long training sequence (LTS) 159 and 161, a signal field (SIG 1) 224, a data field or another signal field 228, and two guard intervals 220, 226. In this embodiment, the symbols of the STS 157 are divided into two sets 232, 234. The first set 232 is included in the first antenna frame 104-1 and the second set of symbols 2324 is included in the second antenna frame 104-2. The figure includes an example of a dividing the symbols into sets 232, 234, where, in one embodiment, the STS 157 includes 10 symbols as per previous versions of the IEEE 802.11x specification. The LTS 159 and 161 of the first antenna frame 104-1 includes a double guard interval (GI2) 236 that may be 1600 nanoseconds in duration and corresponds to the last 1600 nanoseconds of the LTS prepended to the LTS.

The LTS 159 and 161 includes a twice repeating long training sequence that may correspond to previous versions of the IEEE 802.11x specification and, wherein, tones of the LTS are divided into two sets 238, 240. The first set of tones 238 is included in the first antenna frame 104-1 and the second set of tones 240 is included in the second antenna frame 104-2.

FIG. 11 is a diagram of a preamble of frames 104-1, -2, -3 using cyclic shifting for three transmit antennas, where the communication devices are in a proximal area that only includes IEEE 802.11n compliant devices. The preamble is part of the wireless communication set up information 106 and includes a short training sequence (STS) 157, a long training sequence (LTS) 159 and 161, a signal field (SIG 1) 224, a data field or another signal field 228, and two guard intervals 220, 226. For the first antenna frame 104-1, the STS 157 is divided into three sets of symbols 250, 252, 254. In one embodiment, the STS 157 includes 10 symbols of 800 nanoseconds as per previous versions of the IEEE 802.11x specification, where, for example, the first set 250 includes symbols 0-2, the second set 252 includes symbols 3-5, and the third set 254 includes symbols 6-9. As one of ordinary skill in the art will appreciate, other groupings of the symbols may be used.

The LTS 159 and 161 of the first antenna frame 104-1 includes a double guard interval (GI2) 236 that may be 1600 nanoseconds in duration and corresponds to the last 1600 nanoseconds of the LTS prepended to the LTS 159 and 161. The LTS 159 and 161 includes a twice repeating long training sequence that may correspond to previous versions of the IEEE 802.11x specification and, wherein, tones of the LTS are divided into three sets 256, 258, 260. The signal field 224 and the optional second signal field 238 contain information as previously discussed.

The preambles for the second and third antenna frames 104-2, -3 include similar components to the preamble of the first antenna frame 104-1, but with the STS 157 and/or LTS 159 and 161 being cyclic shifted. As shown, the three sets of symbols 250, 252, 254 are shifted, in time, with respect to each antenna frame 104-1, -2, -3. In one embodiment, the cyclic shift may be 400-1600 nanoseconds.

Each LTS pattern of the LTS field 159 and 161 may be divided into three sets 256, 258, 260 as shown, where the first set of tones 256 precedes, in time, the second and third sets of tones 258, 260 for the first antenna frame 104-1, for the second antenna frame 104-2, the second set 258 precedes, in time, the first and third sets 256, 260, and for the third antenna frame 104-3, the third set 260 precedes, in time, the first and second sets 256, 258. As such, the LTS 159 and 161 of the second and third antenna frames 104-2, -3 is cyclic shifted with respect to the LTS 159 and 161 of the first antenna frame 104-1.

FIG. 12 is another diagram of a preamble of frames 104-1, -2, -3 using cyclic shifting for three transmit antennas that include a legacy portion and a supplemental portion. The legacy portion includes the STS 157, which may be divided into three sets of symbols 250, 252, 254, and an LTS section 159 and 161, which may be divided into two sets of tones 238, 240. The supplemental section includes a guard interval 274 and only one LTS pattern, which includes first and second set of tones 276, 278.

In this embodiment, s1 . . . s2 are k*200 nanosecond cyclic shifts of s0, where k=1 . . . 2 and s0-s2 correspond to the symbols of the STS field 157 of the respective antenna frames 104-1, -2, -3. The first and second set of tones 238, 240 of the LTS 159 and 161 correspond to two legacy IEEE 802.11a long training symbols (3.2 microsecond each plus 1.6 microsecond prepended GI2 236), where each pairing of the first and second sets 238, 240 are equal. The first and second sets of tones 238, 240 of the LTS 159 and 161 for the second antenna frame 104-2 are each 1.6-microsecond cyclic shifts of the first and second sets of tones 238, 240 for the first antenna frame 104-1. The supplemental LTS for the third antenna frame 104-3 is a copy of the first and second sets 238, 240 of one LTS pattern of the first antenna frame 104-1 with GI2 274 (the last 1.6 microseconds) prepended. Only the first data symbol (DATA0) 272 has GI2 270 (the last 1.6 microseconds) prepended. All subsequent data symbols have just GI (the last 800 nanoseconds) prepended. The GI2 fields 274 prior to the supplemental LTS and GI2 field 270 prior to the first data symbol (DATA0) are used to allow settling of the power amplifiers.

FIG. 13 is a diagram of a preamble of frame using a form of cyclic shifting that includes sparse symbols and/or tones for three transmit antenna frames 104-1, -2, -3, where the communication devices are in a proximal area that only includes IEEE 802.11n compliant devices. The preamble is part of the wireless communication set up information 106 and includes a short training sequence (STS) 157, a long training sequence (LTS) 159 and 161, a signal field (SIG 1) 224, a data field or another signal field 228, and two guard intervals 220, 226. In this embodiment, the symbols of the STS 157 are divided into three sets 280, 282, 284. The first set 280 is included in the first antenna frame 104-1, the second set of symbols 282 is included in the second antenna frame 104-2, and the third set of symbols 284 is included in the third antenna frame 104-3. The figure includes an example of a dividing the symbols into sets, where, in one embodiment, the STS 157 includes 10 symbols as per previous versions of the IEEE 802.11x specification. In such an example, the first set 280 may include symbols 0, 3, 6, the second set may include symbols 1, 4, 7, and the third set 284 may include symbols 2, 5, 8.

The LTS 159 and 161 of the first antenna frame 104-1 includes a double guard interval (G12) 236 that may be 1600 nanoseconds in duration and corresponds to the last 1600 nanoseconds of the LTS prepended to the LTS 161. The LTS includes a twice repeating long training sequence 159 and 161 that may correspond to previous versions of the IEEE 802.11x specification and, wherein, tones of the LTS are divided into three sets 286, 288, 290. The first set of tones 286 is included in the first antenna frame 104-1, the second set of tones 288 is included in the second antenna frame 104-2, and the third set of tones 290 is included in the third antenna frame 104-3. For example, if a long training sequence includes 15 tones, the first set 286 may include tones 0, 3, 6, 9, 12, the second set 288 may include tones 1, 4, 7, 10, 13, and the third set 290 may include tones 2, 5, 8, 11, 14.

FIG. 14 is a diagram of preambles of frames 104-1, -2, -3, -4 using cyclic shifting for four transmit antennas. As shown, the STS 157 may be divided into four sets of symbols 300, 302, 304, 306 and/or the LTS 159 and 161 may be divided into four sets of tones 308, 310, 312, 314. For each antenna frame 104-1, -2, -3, -4, the set of symbols 300, 302, 304, 306 are cyclically shifted and/or the set of tones 308, 310, 312, 314 are cyclically shifted.

FIG. 15 is another diagram of preambles of frames 104-1, -2, -3, -4 using cyclic shifting for four transmit antennas. In this embodiment, s1 . . . s3 are k*200 nanosecond cyclic shifts of s0, where k=1 . . . 3, where s0-s3 correspond to the sets of symbols 300, 302, 304, 306 of the STS 157. The LTS 159 and 161 and signal field 224 for the first and second antenna frames 104-1, -2 are as discussed with reference to FIG. 12. The supplemental LTS for the third antenna frame 104-2 includes the first and second sets 238, 240, which may be copies of sets 238, 240 of the LTS 159 and 161 for the first antenna frame 104-1, with G12 236 (the last 1.6 microseconds) prepended. The supplemental LTS for the fourth antenna frame 104-4 includes the first and second sets 230, 240 of the LTS for the second antenna frame 104-2 with G12 236 (the last 1.6 microseconds) prepended. In other words, the LTS of the fourth antenna frame 104-4 is a 1.6-microsecond cyclic shift of the supplemental LTS of the third antenna. The first data symbol (DATA0) 272 has GI2 270 (the last 1.6 microseconds) prepended. All subsequent data symbols have just GI (the last 800 nanosecond) prepended.

FIG. 16 is a diagram of a preamble of frame using a cyclic shifting that uses sparse symbols and/or tones for four transmit antennas, where the communication devices are in a proximal area that only includes IEEE 802.11n compliant devices. The preamble is part of the wireless communication set up information 106 and includes a short training sequence (STS) 157, a long training sequence (LTS) 159 and 161, a signal field (SIG 1) 224, a data field or another signal field 228, and two guard intervals 220, 226. In this embodiment, the symbols of the STS 157 are divided into four sets 320, 322, 324, 326. The first set 320 is included in the first antenna frame 104-1, the second set of symbols 322 is included in the second antenna frame 104-2, the third set of symbols 324 is included in the third antenna frame 104-3, and the fourth set of symbols 326 is included in the fourth antenna frame 104-4. The figure includes an example of a dividing the symbols into sets, where, in one embodiment, the STS includes 10 symbols as per previous versions of the IEEE.11× specification. For example, the first set 320 may includes symbols 0, 4, the second set 322 may include symbols 1, 3, the third set may include symbols 2, 6, and the fourth set 326 may include symbols 3, 7.

The LTS 159 and 161 of the first antenna frame 104-1 includes a double guard interval (GI2) 236 that may be 1600 nanoseconds in duration and corresponds to the last 1600 nanoseconds of the LTS prepended to the LTS. The LTS includes a twice repeating long training sequence 159 and 161 that may correspond to previous versions of the IEEE 802.11x specification and, wherein, tones of the LTS are divided into four sets 328, 330, 332, 334. The first set of tones 328 is included in the first antenna frame 104-1, the second set of tones 330 is included in the second antenna frame 104-2, the third set of tones 332 is included in the third antenna frame 104-3, and the fourth set of tones 334 is included in the fourth antenna frame 104-4. For example, if the long training sequence includes 20 tones, the first set 328 may include tones 0, 4, 8, 12, 16, the second set 330 may include tones 1, 5, 9, 13, 17, the third set 332 may include tones 2, 6, 10, 14, 18, and the fourth set 334 may include tones 3, 7, 11, 15, 19. Note that the supplemental LTS fields may be used such that the tones of an LTS pattern are only divided into two sets of tones.

FIG. 17 is a diagram of a wireless communication between two wireless communication devices 100 and 102, each of which is compliant with IEEE 802.11n. Such a communication is taking place within a proximal area that includes IEEE 802.11n compliant devices, IEEE 802.11a compliant devices and/or IEEE 802.11g compliant devices. In this instance, the wireless communication may be direct or indirect where a frame 110 includes a legacy portion of the set-up information 112, remaining set-up information portion 114, and the data portion 108.

The legacy portion of the set-up information 112 includes a short training sequence 157, which is 8 microseconds in duration, a long training sequence 171, which is 8 microseconds in duration, and a signal field 173, which is 4 microseconds in duration. The signal field 173, as is known, includes several bits to indicate the duration of the frame 110. As such, the IEEE 802.11a compliant devices within the proximal area and the IEEE 802.11g compliant devices within the proximal area will recognize that a frame is being transmitted even though such devices will not be able to interpret the remaining portion of the frame. In this instance, the legacy devices (IEEE 802.11a and IEEE 802.11g) will avoid a collision with the IEEE 802.11n communication based on a proper interpretation of the legacy portion of the set-up information 112.

The remaining set-up information 114 includes additional supplemental long training sequences 159, 161, which are each 4 microseconds in duration. The remaining set-up information further includes a high data signal field 163, which is 4 microseconds in duration to provide additional information regarding the frame. The data portion 108 includes the data symbols 165, 167, 169, which are 4 microseconds in duration as previously described with reference to FIG. 7. In this instance, the legacy protection is provided at the physical layer.

FIG. 18 is a diagram of a wireless communication between two wireless communication devices 100 and 102, each of which is compliant with IEEE 802.11n. Such a communication is taking place within a proximal area that includes IEEE 802.11n compliant devices, IEEE 802.11a compliant devices and/or IEEE 802.11g compliant devices. In this instance, the wireless communication may be direct or indirect where frames 110-1, 110-2, 110-N each includes a legacy portion of the set-up information 112, remaining set-up information portion 114, and the data portion 108 using multiple antennas.

The legacy portion of the set-up information 112 includes a short training sequence 157, which is 8 microseconds in duration, a long training sequence 171, which is 8 microseconds in duration, and a signal field 173, which is 4 microseconds in duration. The signal field 173, as is known, includes several bits to indicate the duration of the frame 110. As such, the IEEE 802.11a compliant devices within the proximal area and the IEEE 802.11g compliant devices within the proximal area will recognize that a frame is being transmitted even though such devices will not be able to interpret the remaining portion of the frame. In this instance, the legacy devices (IEEE 802.11a and IEEE 802.11g) will avoid a collision with the IEEE 802.11n communication based on a proper interpretation of the legacy portion of the set-up information 112.

The remaining set-up information 114 includes additional supplemental long training sequences 159, 161, which are each 4 microseconds in duration. The remaining set-up information further includes a high data signal field 163, which is 4 microseconds in duration to provide additional information regarding the frame. The data portion 108 includes the data symbols 165, 167, 169, which are 4 microseconds in duration as previously described with reference to FIG. 7. In this instance, the legacy protection is provided at the physical layer.

In one embodiment, m is the number of longer training sequences per frame, N is the number of transmit antennas, the preamble (sometimes referred to as “Brownfield”) is for the case when 0.11a or 0.11g legacy devices present. The short training and long training sequences are the same as IEEE 802.11a for TX antenna 1. For antennas 2 to N there are two possibilities:

-   -   Use a cyclic shifted version of the same sequence. The amount of         cyclic shift per antenna is computed from (Antenna         number−1)*800/N in nanoseconds for the short training and         (Antenna number−1)*4/N in microseconds.

A second mode is to leave the short training through signal field parts transmitted on antennas 2-to-N as null. (i.e. these antennas do not transmit during this interval.) Furthermore, supplemental long training sequences from antenna 1 are not used and nothing is transmitted during this time.

The signal field 173 will follow the same format as IEEE 802.11a, except the reserved bit (4) will be set to 1 to indicate an IEEE 802.11n frame and subsequent training for 0.11n receivers. The supplemental training long training sequences can be defined in multiple ways:

-   -   (m=1) For this case, there will only be one long supplemental         training sequence 159. It will be orthogonal to the IEEE 802.11a         long training sequence.     -   (m=N−1) For this case, the number of training sequences is equal         to the number of transmit antennas. This is preferable to the         (m=1) case because it will lead to less channel estimation error         at the receiver, especially for large numbers of antennas. Thus,         it is scalable.

There are three possible choices of training sequence:

-   -   Zero space—In this case, sequences (1,1), (2,2), (3,3), . . . up         to (m,m) are the same as the IEEE 802.11a long training         sequence. All others (i.e. (1,2), (2,1), etc) are null—nothing         is transmitted during that time slot.)     -   Subchannel null—In this case, the set of sub-channels in the         training sequences is sub-divided by the number of transmit         antennas. Individual subsets are activated on each sub-training         interval.

One embodiment uses Orthogonal sequences that are generated by multiplying the IEEE 802.11a long training sequence by an m×m orthonormal matrix, such as the matrix which generates a discrete Fourier transform, as will be described in greater detail with reference to FIGS. 29-32. For example, the 4 antenna case would employ the following orthonormal matrix to generate the subcarriers for each supplemental long training sequence.

$\begin{matrix} {S_{k} = \begin{bmatrix} s_{10,k} & s_{11,k} & s_{12,k} \\ s_{20,k} & s_{21,k} & s_{22,k} \\ s_{30,k} & s_{31,k} & s_{32,k} \end{bmatrix}} \\ {{= \begin{bmatrix} s_{00,k} & {s_{00,k} \cdot ^{ \cdot \theta_{k}}} & {s_{00,k} \cdot ^{ \cdot \varphi_{k}}} \\ s_{00,k} & {s_{00,k} \cdot ^{ \cdot {({\theta_{k}\frac{4 \cdot \pi}{3}})}}} & {s_{00,k} \cdot ^{ \cdot {({\varphi_{k}\frac{2 \cdot \pi}{3}})}}} \\ s_{00,k} & {s_{00,k} \cdot ^{ \cdot {({\theta_{k}\frac{2 \cdot \pi}{3}})}}} & {s_{00,k} \cdot ^{ \cdot {({\varphi_{k}\frac{4 \cdot \pi}{3}})}}} \end{bmatrix}}{\theta_{k} = {\pi \cdot {k/\left( {4 \cdot N_{subcarriers}} \right)}}}{\varphi_{k} = {\pi \cdot {\left( {k + 4} \right)/\left( {2 \cdot N_{subcarriers}} \right)}}}} \end{matrix}$

FIG. 19 is a diagram of preambles of frames 104-1, -2 using cyclic shifting for two transmit antennas using a legacy portion. The STS 157 is divided into two sets of symbols 344, 346 as shown. For example, the first set 344 may include symbols 0-4, and the second set 346 may include symbols 5-9. The next portion of the preamble for the first antenna frame 104-1 includes a legacy LTS 340, guard interval 220, and a signal field 224. The supplemental LTS 342 for the second antenna frame 104-2 is identical to the LTS of the first antenna frame, but shifted in time.

FIG. 20 is a diagram of preambles of frames 104-1, 104-2, 104-3 using cyclic shifting for three transmit antennas using a legacy portion. The STS 157 is divided into three sets of symbols 250, 252, 254 as shown and as previously discussed. The next portion of the preamble for the first antenna frame 104-1 includes a legacy LTS 340, a guard interval 220, and a signal field 224. The supplemental LTS 342 for the second antenna frame 104-2 is identical to the LTS of the first antenna frame, but shifted in time. The supplemental LTS for the third antenna frame 104-2 is cyclic shifted version of the supplemental LTS of the second antenna. All three frames 104-1, -2, -3 further include a double guard interval 336 and a data field 228.

FIG. 21 is a diagram of preamble of frames 104-1, -2, -3, -4 using cyclic shifting for four transmit antennas using a legacy portion. The STS 157 is divided into four sets of symbols 300, 302, 304, 306 as shown and as previously discussed. The next portion of the preamble for the first antenna frame 104-1 includes a legacy LTS 340, a guard interval 220, and a signal field 224. The supplemental LTS 342-1 for the second antenna frame 104-2 is identical to the LTS of the first antenna frame 104-1, but shifted in time. The supplemental LTS 342-1 for the third antenna frame 104-3 is cyclic shifted version of the supplemental LTS 342-1 of the second antenna frame 104-2. The supplemental LTS 342-2 for the fourth antenna frame 104-4 includes only one LTS pattern 264 of the legacy LTS, is time shifted as shown, and is approximately 40 in duration.

FIG. 22 is a diagram of a wireless communication between two wireless communication devices 100 and 102 that are both IEEE 802.11n compliant. The wireless communication may be direct or indirect within a proximal area that includes IEEE 802.11 compliant devices, IEEE 802.11a, IEEE 802.11b and/or IEEE 802.11g devices. In this instance, the frame 111 includes a legacy portion of the set-up information 112, remaining set-up information 114 and the data portion 108. As shown, the legacy portion of the set-up information 112, or legacy frame, includes an IEEE 802.11 PHY preamble (i.e., STS 157, LTS 171, and signal field 173) and a MAC partitioning frame portion 175, which indicates the particulars of this particular frame that may be interpreted by legacy devices. In this instance, the legacy protection is provided at the MAC layer.

The remaining set-up information 114 includes a plurality of supplemental long training sequences 159, 161 and the high data signal field 163. The data portion 108 includes a plurality of data symbols 165, 167, 169 as previously described.

FIG. 23 is a diagram of a wireless communication between two wireless communication devices 100 and 102 that are both IEEE 802.11n compliant using multiple antennas. The wireless communication may be direct or indirect within a proximal area that includes IEEE 802.11 compliant devices, IEEE 802.11a, IEEE 802.11b and/or IEEE 802.11g devices. In this instance, each of the frames 111-1, 111-2, 111-N includes a legacy portion of the set-up information 112, remaining set-up information 114 and the data portion 108. As shown, the legacy portion of the set-up information 112, or legacy frame, includes an IEEE 802.11 PHY preamble (i.e., STS 157, LTS 171, and signal field 173) and a MAC partitioning frame portion 175, which indicates the particulars of this particular frame that may be interpreted by legacy devices. In this instance, the legacy protection is provided at the MAC layer. Note that the fields follow the same structure as for FIGS. 9 and 10 described above, with the exception of the signal field. This is an alternative that uses MAC partitioning to set the NAV of legacy stations. The MAC partitioning segment contains frame information, coded at a legacy rate to allow reception by IEEE 802.11a and IEEE 802.11g stations. The definitions of the supplemental long training symbols 159, 161 follows the same format as in the previous FIG. 9.

The remaining set-up information 114 includes a plurality of supplemental long training sequences 159, 161 and the high data service field 163. The data portion 108 includes a plurality of data symbols 165, 167, 169 as previously described.

FIG. 24 is a method for multiple protocol wireless communications in a WLAN. The method begins at step 120, where an access point (for indirect wireless communications) or a wireless communication device (for direct wireless communications), determines protocols of wireless communication devices within a proximal region. In an embodiment, the protocols may be determined based on frequency band of use and wireless local area network communication format of each of the wireless communication devices. For example, if the frequency band is 2.4 GHz, a device may have a WLAN communication format in accordance with IEEE 802.11b, IEEE 802.11g, and/or IEEE 802.11n. If the frequency band is 4.9-5.85 GHz, a device may have a WLAN communication format in accordance with IEEE 802.11a or IEEE 802.11n. Further, the proximal region includes coverage area of a basic service set, coverage area of an ad-hoc network, and/or coverage area of the basic service set and at least a portion of at least one neighboring basic service set. With reference to FIG. 1, neighboring BSS of access point 12 include the BSS of access point 14 and/or the BSS of access point 16.

Returning to the logic diagram of FIG. 24, the process continues at step 122 where the access point and/or the wireless communication device determines whether the protocols of the wireless communication devices within the proximal region are of a like protocol. The process then proceeds to step 124 where the process branches depending on whether the protocols of the wireless communication devices within the proximal region are of a like protocol. When the wireless communication devices within the proximal region all use the same protocol, the process proceeds to step 126 where the wireless communication devices use their protocol for setting up a wireless communication and for the wireless communication.

If, however, at least one wireless communication device has a different protocol, the process proceeds to step 128 where the access point or a wireless communication device selects a protocol of the protocols of the wireless communication devices within the proximal region based on a protocol ordering to produce a selected protocol. The protocol ordering may be an ordering of the protocols based on legacy ordering of wireless communication devices and/or an ordering of the protocols based on a transmission efficiency ordering of the protocols. For example, IEEE 802.11, IEEE 802.11b, IEEE 802.11g, and IEEE 802.11n compliant devices operate in the 2.4 GHz frequency band and IEEE 802.11a and IEEE 802.11n compliant devices operate in the 4.9-5.85 GHz frequency band. Thus, in the 2.4 GHz frequency band, if IEEE 802.11b stations are present with IEEE 802.11n device, MAC level protection mechanisms, such as those defined in IEEE 802.11g, and as shown in FIG. 6, may be used. However, if the only legacy IEEE.11g devices are present with IEEE 802.11n devices, then either MAC level (e.g., FIG. 6) or PHY level (e.g., FIG. 5) protection mechanisms may be used. In the 4.9-5.85 GHz frequency band, if IEEE 802.11a devices are present with IEEE.11n devices, the MAC level protection mechanism or the PHY level protection mechanism may be used.

As one of average skill in the art will appreciate, it may be more desirable to use a PHY level protection mechanism, than a MAC level protection mechanism because the throughput impact will be less since the additional frames of the MAC level protection are not needed. Thus, when possible, the PHY mechanism should be employed first. If the PHY mechanism does not work well, as measured by the number of unacknowledged frames exceeding a threshold, then the MAC level mechanism should be employed.

As one of average skill in the art will further appreciate, the legacy status and required use of protection mechanisms can be enabled in the ERP Information Element of the beacon frame (and probe response frame). Currently IEEE 802.11g uses bits 0 to indicate Non-ERP (i.e. 0.11b) present and bit 1 to force stations to Use Protection (MAC level). This can be extended to used the reserved bits (3 though 7) to indicate legacy status of IEEE 802.11g or IEEE 802.11a stations. In one embodiment, bit 3 may be used to indicate “Legacy OFDM present”. The bits would then be interpreted as follows:

Bit 0 - Non ERP Bit 1 - Use Bit 3 - Legacy Present Protection OFDM Present Action for 802.11n 0 0 0 Use .11n frames 1 1 0 Use MAC protection 1 1 1 Use MAC protection 0 1 1 Use PHY or MAC protection 0 0 1 Optionally use PHY or MAC Protection For IEEE 802.11n the MAC level protection mechanisms are the same as for IEEE 802.11g. Stations should either use CTS to self or a CTS/RTS exchange to set the NAV (network allocation vector) of legacy stations.

Returning the logic diagram of FIG. 24, the processing continues at step 130 where the wireless communication device utilizes the selected protocol within the proximal region to set up a wireless communication within the proximal region. This was illustrated in the previous Figures. The process then proceeds to step 132 where the wireless communication device uses its protocol for a data transmission of the wireless communication.

FIG. 25 is a logic diagram of method for determining whether the selected protocol should be changed. The processing begins at step 140 where the access point and/or the wireless communication devices, monitors data transmissions within the proximal region for unacknowledged data transmissions. The process proceeds to step 142 where the access point and/or the wireless communication device compares the unacknowledged data transmission with a transmission failure threshold (e.g., up to 5%). If the comparison is favorable, the process proceeds to step 146 where the selected protocol remains unchanged and the process repeats at step 140.

If, however, the comparison at step 144 was unfavorable, the process proceeds to step 148 where the access point and/or the wireless communication device selects another one of the protocols of the wireless communication devices within the proximal region based on the protocol ordering to produce another selected protocol. For example, the MAC layer protection mechanism may be selected to replace the PHY layer protection mechanism when too many transmission failures occur. The process then proceeds to step 150 where the wireless communication devices uses the another selected protocol within the proximal region to set up the wireless communication within the proximal region.

FIG. 26 is a logic diagram of a method for a wireless communication device to participate in multiple protocol wireless communications. The process begins at step 160 where the wireless communication device affiliates with an access point utilizing a protocol (e.g., IEEE 802.11n) of the wireless communication device. The process then proceeds to step 162 where the wireless communication device receives a selected protocol from the access point. Note that the selected protocol and the protocol of the wireless communication device may be a wireless local area network communication formats in accordance with IEEE 802.11, IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.11n and/or further versions of the IEEE 802.11. Further note that the selected protocol includes a first frame format that includes a legacy header and a Media-Specific Access Control (MAC) layer partitioning field, a second frame format that includes a physical (PHY) layer backward compatible header, and/or a third frame format that includes a current version header and the MAC layer partitioning field.

The process then proceeds to step 164 where the wireless communication device determines whether the selected protocol and the protocol of the wireless communication device are of a like protocol. The process branches at step 166 to step 168 when the protocols are the same and to step 170 when the protocols are not the same. At step 168, the wireless communication device utilizes the protocol to set up a wireless communication and to transfer data. At step 170, the wireless communication device utilizes the selected protocol to set up a wireless communication. The process then proceeds to step 172 where the wireless communication device utilizes the protocol of the wireless communication device for the wireless communication.

FIG. 27 is a logic diagram of a method for a wireless communication device to participate in multiple protocol wireless communications. The process begins at step 180 where the wireless communication device receives a frame via a wireless channel. The process then proceeds to step 182 where the wireless communication device determines whether a selected protocol is not of a like protocol of the wireless communication device. When the selected protocol is the same as the protocol of the wireless communication device, the process proceeds to step 184 where the wireless communication device uses its protocol to set up a wireless communication and to transmit data.

If, however, the selected protocol is not the same as the protocol of the wireless communication device, the process proceeds to step 186 where the wireless communication device uses the selected protocol to interpret at least a portion of wireless communication set up information of the frame. In one embodiment, the wireless communication device may interpret the set up information by interpreting a header of the frame for conformity with a legacy physical layer format to provide the interpreting of the at least a portion of the wireless communication set up information and, when the header of the frame does not conform with the legacy physical layer format, determining that the remainder of the frame is formatted in accordance with the protocol of the wireless communication device. Note that the legacy physical layer format includes at least one of IEEE 802.11a and IEEE 802.11g and wherein the protocol of the wireless communication device includes IEEE 802.11n.

In another embodiment, the wireless communication device may interpret the set up information by interpreting the frame for conformity with a legacy Media-Specific Access Control (MAC) layer format to provide the interpreting of the at least a portion of the wireless communication set up information and, when the header of the frame does not conform with the legacy MAC layer format, determining that the remainder of the frame is formatted in accordance with the protocol of the wireless communication device. Note that the legacy physical layer format includes at least one of IEEE 802.11a, IEEE 802.11b, and IEEE 802.11g and wherein the protocol of the wireless communication device includes IEEE 802.11n.

The process then proceeds to step 188 where the wireless communication device, based on the interpreting of the at least a portion of the wireless communication set up information, determines whether a remainder of the frame is formatted in accordance with the protocol of the wireless communication device. The process then branches at step 190 to step 194 when the remainder of the frame is formatted in accordance with the protocol of the wireless communication device and to step 192 when it does not. At step 192 the wireless communication device ignores the frame. At step 194, the wireless communication device processes the remainder of the frame based in accordance with the protocol of the wireless communication device.

FIG. 28 is a logic diagram of a method for a wireless communication device to participate in multiple protocol wireless communications. The method begins at step 200 where the wireless communication device determines whether a selected protocol is of a like protocol of the wireless communication device. The process branches at step 202 to step 204 when the selected protocol is the protocol of the wireless communication device and to step 206 when the protocols differ. At step 204, the wireless communication device formats the set up information portion of a frame and a data portion of the frame in accordance with its protocol. The wireless communication device then transmits the frame.

If, however, the selected protocol is not of the like protocol of the wireless communication device, the process proceeds to step 206 where the wireless communication device formats a portion of wireless communication set up information in accordance with the selected protocol to produce legacy formatted set up information. The process then proceeds to step 208 where the wireless communication device formats remainder of the wireless communication set up information in accordance with the protocol of the wireless communication device to produce current formatted set up information. The process then proceeds to step 210 where the wireless communication device formats data in accordance with the protocol of the wireless communication device to produce current formatted data. Refer to the previous Figures for examples of such formatting. The process then proceeds to step 212 where the wireless communication device transmits a frame containing the legacy formatted set up information, the current formatted set up information, and the current formatted data.

In an embodiment of the present invention, the preamble should be backward compatible with existing IEEE 802.11 standards. An issue in TGn is how to interoperate with legacy IEEE 802.11a and IEEE 802.11b/g devices, where interoperation includes two cases:

-   -   Same BSS: All devices communicating with the same AP.     -   Co-channel/“overlapping” BSS         Such can be addressed by either design the PLCP header to allow         an IEEE 802.11a/g STA to de-assert CCA or use a protection         mechanism like RTS/CTS or CTS-to-self.     -   IEEE 802.11g chose the latter in dealing with IEEE 802.11b         devices.     -   To some extent, RTS/CTS can be relied on to protect bursts         anyway.

For unchanged SIGNAL field decoding at legacy stations, it is desirable to use the same linear weighting of the existing long training and SIGNAL symbols at the transmitter antenna inputs. With a MISO system, the same weighting should be applied to the first two long training symbols and the legacy SIGNAL field for decoding by legacy stations.

For the case of M transmitter antennas, N receiver antennas and a sequence of L transmitted symbols, Xk is the received signal on sub-carrier k:

The zero-forcing (ZF) MIMO channel estimate is then computed as:

${\hat{H}}_{k} = {{\left( {S_{k}^{H} \cdot S_{k}} \right)^{- 1} \cdot S_{k}^{H} \cdot X_{k}} = {\frac{1}{M\;} \cdot S_{k}^{H} \cdot X_{k}}}$

if the long training symbol sequence is defined well (i.e., Sk ends up being a real scalar times a unitary matrix).

The minimum mean-square error (MMSE) channel estimate is computed as:

Ĥ_(k) = (S_(k)^(H) ⋅ S_(k) + σ_(η)² ⋅ I)⁻¹ ⋅ S_(k)^(H) ⋅ X_(k) = ρ ⋅ S_(k)^(H) ⋅ X_(k) $\rho = \frac{1}{M + \sigma_{\eta}^{2}}$

where, for simplicity, hk was assumed to be i.i.d. Gaussian and, again, use the “good long training choice”. Note that performance of the MMSE versus ZF estimation may be omitted for the sequences chosen in the following, since S was carefully chosen as previously shown.

FIG. 29 is a diagram illustrating simultaneous second channel sounding with a transmission model of the frame format 104 of FIG. 7. The frame format 104 includes a carrier detect 225, channel sounding symbols 227, a signal field (SIG) 229, and a signal field (SIG 2) 231. By way of example, further frames are illustrated as formed via a multiple antenna next generation MIMO transmitter. These frames include carrier detect 233, channel sounding symbols (2,2) 253, channel sounding (2,L) 237, signal field (SIG 2) 239, and carrier detect 241, channel sounding (M,2) 243, channel sounding symbols (M,2) 245, and signal field (SIG 2) 247, which are discussed in additional detail with reference to FIGS. 30-32. The carrier detect 225, 233, and 241 are short symbols sent during a “Carrier Detect” period. “Carrier Detect” symbols for antennas 2 . . . M are generally equivalent for as those transmitted on a first antenna, except cyclically shifted.

The first channel sounding symbols 227 and signal field (SIG) 229 include the long training symbols and signal field of legacy systems, and are transmitted from a first antenna. These are used for computing an estimate of the channel from the first transmit antenna to the receiver antennas. The second channel sounding symbols 235, 243, are transmitted on antennas 2 . . . M and are used for computing an estimate of the channel from the second transmit antennas to the receiver antennas.

The signal fields (SIG 2) 239 and 247 includes the IEEE 802.11n rate and frame length information. Average output power is scaled to be constant throughout the frame, averaged across the transmit antennas. For this transmission format, in order to satisfy backwards compatibility issues and also to satisfy the requirements of the next generation channel estimation requirements, a weighting factor W is chosen such that W and W−1 are simple to implement. Further, any beam forming issues from MIMO transmitters (next generation devices) by [w11 . . . w1M] should be well-received by legacy IEEE 802.11a/g devices.

In this embodiment, referring also to FIG. 30, which is another diagram of simultaneous second channel sounding, a channel sounding (S_(k)) 253 is multiplied by a plurality of weighting factors (W_(k, m)) 301, 303, 305, wherein k corresponds to the channel sounding number, which ranges from 1 to L, and M corresponds to the number of transmit antennas 82-86. The resulting weighted channel soundings are converted to RF signals via the transmitters 67, 69, 71 and subsequently transmitted via the antennas 81, 83, 85. In such an embodiment, a weighting factor matrix may be as follows:

$\begin{bmatrix} w_{11} & w_{12} & \ldots & w_{1,M} \\ w_{21} & w_{22} & \ldots & w_{2,M} \\ \vdots & \vdots & \ddots & \vdots \\ w_{L\; 1} & w_{L\; 2} & \ldots & w_{LM} \end{bmatrix}s_{k}$

With transmissions occurring on all antennas at all times, nulls may be formed. The nulls may be compensated for by selecting a weight sequence that acts as a beam former such that the nulls are steered in particular directions. For example, for the case of the vector w1=[1 1] (one row of the previous side's W matrix for a two-TX case), nulls would be steered in the directions−90° and +90°. Thus, certain directions are disadvantaged versus others at a single-input receiver of a legacy WLAN device.

According to the present invention, a different complex weight is applied to each subcarrier on M−1 of the transmit antennas. This forms a different beam pattern on each subcarrier and results in less power and capacity loss in the worst directions. This is illustrated in FIGS. 31 and 32.

FIG. 31 is a diagram illustrating the manner in which a preamble of the frame format of FIG. 7 is formed for a generalized next generation MIMO transmitter and particularly for a two antenna next generation MIMO transmitter. In this illustration, two preambles are generated: one for each active antenna. The first preamble 311, which is transmitted by the first antenna, includes a double guard interval (GI2) 313, a first channel sounding (CS 0,0) 315, a second channel sounding (CS 0,1) 317, a guard interval (GI) 319, a signal field (SIG) 321, another guard interval (GI) 323, and a third channel sounding (CS 0,2) 325. The second preamble 327, which is transmitted by the second antenna, includes a double guard interval (GI2) 329, a first channel sounding (CS 1,0) 331, a second channel sounding (CS 1,1) 333, a guard interval (GI) 335, a signal field (SIG) 337, another guard interval (GI) 339, and a third channel sounding (CS 1,2) 341.

In this embodiment, the following may be used for the various channel soundings:

S ₀₁ =S ₀₀

S _(10,k) =−S _(00,k) ·e ^(i·θ) ^(k)

S ₁₁ =S ₁₀

S ₀₂ =S ₀₀

S _(12,k) =S _(00,k) ·e ^(i·θ) ^(k)

From these channel soundings, the weighting factor may be applied as follows:

$\begin{matrix} {S_{k} = \begin{bmatrix} s_{10,k} & s_{11,k} \\ s_{20,k} & s_{21,k} \end{bmatrix}} \\ {= {s_{00,k} \cdot \begin{bmatrix} 1 & {- 1} \\ 1 & 1 \end{bmatrix} \cdot \begin{bmatrix} 1 & 0 \\ 0 & ^{ \cdot \theta_{k}} \end{bmatrix}}} \\ {= \begin{bmatrix} s_{00,k} & {{- s_{00,k}} \cdot ^{ \cdot \theta_{k}}} \\ s_{00,k} & {s_{00,k} \cdot ^{ \cdot \theta_{k}}} \end{bmatrix}} \end{matrix}$

where the first digital of the subscript of a channel sounding corresponds to the number of antennas, the second digit corresponds to the number of symbols, and the k corresponds to the number of channel soundings. For example, S_(10, k) corresponds to the first symbol transmitted on the first antenna for the kth channel sounding.

To obtain a different beam pattern for each subcarrier, the following is applied:

${\theta_{k} = {\pi \cdot {k/6}}},{k = {{- \frac{N_{subcarriers}}{2}}\ldots \frac{N_{subcarriers}}{2}}}$

FIG. 32 is a diagram illustrating the manner in which a preamble of the frame format of FIG. 7 is formed for a three antenna next generation MIMO transmitter. In this illustration, three preambles are generated: one for each active antenna. The first preamble 351, which is transmitted by the first antenna, includes a double guard interval (GI2) 353, a first channel sounding (CS 0,0) 355, a second channel sounding (CS 0,1) 357, a guard interval (GI) 359, a signal field (SIG) 361, another guard interval (GI) 363, a third channel sounding (CS 0,2) 365, a third guard interval (GI) 367, and a fourth channel sounding (CS 0,3) 369. The second preamble 371, which is transmitted by the second antenna, includes a double guard interval (GI2) 373, a first channel sounding (CS 1,0) 375, a second channel sounding (CS 1,1) 377, a guard interval (GI) 379, a signal field (SIG) 381, another guard interval (GI) 383, a third channel sounding (CS 1,2) 385, a third guard interval (GI) 387, and a fourth channel sounding (CS 1,3) 389. The third preamble 391, which is transmitted by the third antenna, includes a double guard interval (GI2) 393, a first channel sounding (CS 2,0) 395, a second channel sounding (CS 2,1) 397, a guard interval (GI) 399, a signal field (SIG) 401, another guard interval (GI) 403, a third channel sounding (CS 2,2) 405, a third guard interval (GI) 407, and a fourth channel sounding (CS 2,3) 409.

For the various channel soundings, the weighting factor matrix may be applied as follows:

$\begin{matrix} {S_{k} = \begin{bmatrix} s_{10,k} & s_{11,k} & s_{12,k} \\ s_{20,k} & s_{21,k} & s_{22,k} \\ s_{30,k} & s_{31,k} & s_{32,k} \end{bmatrix}} \\ {= \begin{bmatrix} s_{00,k} & {s_{00,k} \cdot ^{ \cdot \theta_{k}}} & {s_{00,k} \cdot ^{ \cdot \varphi_{k}}} \\ s_{00,k} & {s_{00,k} \cdot ^{ \cdot {({\theta_{k}\frac{4 \cdot \pi}{3}})}}} & {s_{00,k} \cdot ^{ \cdot {({\varphi_{k}\frac{2 \cdot \pi}{3}})}}} \\ s_{00,k} & {s_{00,k} \cdot ^{ \cdot {({\theta_{k}\frac{2 \cdot \pi}{3}})}}} & {s_{00,k} \cdot ^{ \cdot {({\varphi_{k}\frac{4 \cdot \pi}{3}})}}} \end{bmatrix}} \end{matrix}$

To obtain a different beam pattern for each subcarrier, the following is applied:

θ_(k) =π·k/6

φ_(k)=π·(k+4)/6

From FIGS. 31 and 32 more signal energy may be transmitted resulting in better channel estimates by the receiver. This enables a more simplified ZF or MMSE channel estimation at Rx (mostly adds/shifts) in that:

$W_{T} = {\left. \begin{bmatrix} {+ 1} & {- 1} \\ {+ 1} & {+ 1} \end{bmatrix}\Rightarrow W_{T}^{- 1} \right. = {\frac{1}{2}\begin{bmatrix} {+ 1} & {- 1} \\ {+ 1} & {+ 1} \end{bmatrix}}}$ $\begin{matrix} {W_{T} = \left. \begin{pmatrix} 1 & 1 & 1 \\ 1 & \frac{{- 1} - {i \cdot \sqrt{3}}}{2} & \frac{{- 1} + {i \cdot \sqrt{3}}}{2} \\ 1 & \frac{{- 1} + {i \cdot \sqrt{3}}}{2} & \frac{{- 1} - {i \cdot \sqrt{3}}}{2} \end{pmatrix}\Rightarrow W_{T}^{- 1} \right.} \\ {= {\frac{1}{3} \cdot \begin{pmatrix} 1 & 1 & 1 \\ 1 & \frac{{- 1} + {i \cdot \sqrt{3}}}{2} & \frac{{- 1} - {i \cdot \sqrt{3}}}{2} \\ 1 & \frac{{- 1} - {i \cdot \sqrt{3}}}{2} & \frac{{- 1} + {i \cdot \sqrt{3}}}{2} \end{pmatrix}}} \end{matrix}$

The channel may be estimated with prior knowledge of the per-subcarrier beamforming coefficients and then these coefficients do not need to be applied to the remaining transmitted symbols. The advantage of this is that no extra multiplications are required on the transmitter side, as the LTRN sequence may simply be looked up in a table.

The channel may be estimated without knowledge of the per-subcarrier beamforming coefficients and then these coefficients should be applied to the remaining transmitted symbols. The advantage of this is that the receiver channel estimation is simplified (fewer multiplies), but the transmitter performs additional multiplications.

First case, using earlier notation and L=M:

${\hat{H}}_{k} = {\frac{1}{M} \cdot s_{00,k}^{*} \cdot W_{B,k}^{H} \cdot W_{T}^{H} \cdot X_{k}}$ $W_{B,k} = {{diag}\left( \left\lbrack {1\mspace{14mu} ^{\frac{ \cdot \pi \cdot l_{1}}{6}}\ldots \mspace{14mu} ^{\frac{ \cdot \pi \cdot l_{M - 1}}{6}}} \right\rbrack \right)}$

Second case, using earlier notation and L=M:

${\hat{H}}_{k} = {\frac{1}{M} \cdot s_{00,k}^{*} \cdot W_{T}^{H} \cdot X_{k}}$

Note that further refinement of the channel estimate is possible by duplicating the entire length-M sequence p times. The refinement may be made by simple averaging. The overhead is identical to the single active transmitter method described on slide 10, but the performance is far superior.

For the backward-compatible preamble case, in which the number of long training symbols is M+1, the longer sequence would consist of p*M+1 long training symbols. There are p identical blocks of M symbols, and the first and second symbols on each antenna are identical.

As one of average skill in the art will appreciate, the term “substantially” or “approximately”, as may be used herein, provides an industry-accepted tolerance to its corresponding term. Such an industry-accepted tolerance ranges from less than one percent to twenty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. As one of average skill in the art will further appreciate, the term “operably coupled”, as may be used herein, includes direct coupling and indirect coupling via another component, element, circuit, or module where, for indirect coupling, the intervening component, element, circuit, or module does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As one of average skill in the art will also appreciate, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two elements in the same manner as “operably coupled”. As one of average skill in the art will further appreciate, the term “compares favorably”, as may be used herein, indicates that a comparison between two or more elements, items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a favorable comparison may be achieved when the magnitude of signal 1 is greater than that of signal 2 or when the magnitude of signal 2 is less than that of signal 1.

The preceding discussion has presented various embodiments for wireless communications in a wireless communication system that includes a plurality of wireless communication devices of differing protocols. As one of average skill in the art will appreciate, other embodiments may be derived from the teachings of the present invention without deviating from the scope of the claims.

Mode Selection Tables

TABLE 1 2.4 GHz, 20/22 MHz channel BW, 54 Mbps max bit rate Code Rate Modulation Rate NBPSC NCBPS NDBPS EVM Sensitivity ACR AACR 1 Barker BPSK 2 Barker QPSK 5.5 CCK 6 BPSK 0.5 1 48 24 −5 −82 16 32 9 BPSK 0.75 1 48 36 −8 −81 15 31 11 CCK 12 QPSK 0.5 2 96 48 −10 −79 13 29 18 QPSK 0.75 2 96 72 −13 −77 11 27 24 16-QAM 0.5 4 192 96 −16 −74 8 24 36 16-QAM 0.75 4 192 144 −19 −70 4 20 48 64-QAM 0.666 6 288 192 −22 −66 0 16 54 64-QAM 0.75 6 288 216 −25 −65 −1 15

TABLE 2 Channelization for Table 1 Frequency Channel (MHz) 1 2412 2 2417 3 2422 4 2427 5 2432 6 2437 7 2442 8 2447 9 2452 10 2457 11 2462 12 2467

TABLE 3 Power Spectral Density (PSD) Mask for Table 1 PSD Mask 1 Frequency Offset dBr −9 MHz to 9 MHz 0 +/−11 MHz −20 +/−20 MHz −28 +/−30 MHz and −50 greater

TABLE 4 5 GHz, 20 MHz channel BW, 54 Mbps max bit rate Code Rate Modulation Rate NBPSC NCBPS NDBPS EVM Sensitivity ACR AACR 6 BPSK 0.5 1 48 24 −5 −82 16 32 9 BPSK 0.75 1 48 36 −8 −81 15 31 12 QPSK 0.5 2 96 48 −10 −79 13 29 18 QPSK 0.75 2 96 72 −13 −77 11 27 24 16-QAM 0.5 4 192 96 −16 −74 8 24 36 16-QAM 0.75 4 192 144 −19 −70 4 20 48 64-QAM 0.666 6 288 192 −22 −66 0 16 54 64-QAM 0.75 6 288 216 −25 −65 −1 15

TABLE 5 Channelization for Table 4 Frequency Frequency Channel (MHz) Country Channel (MHz) Country 240 4920 Japan 244 4940 Japan 248 4960 Japan 252 4980 Japan 8 5040 Japan 12 5060 Japan 16 5080 Japan 36 5180 USA/Europe 34 5170 Japan 40 5200 USA/Europe 38 5190 Japan 44 5220 USA/Europe 42 5210 Japan 48 5240 USA/Europe 46 5230 Japan 52 5260 USA/Europe 56 5280 USA/Europe 60 5300 USA/Europe 64 5320 USA/Europe 100 5500 USA/Europe 104 5520 USA/Europe 108 5540 USA/Europe 112 5560 USA/Europe 116 5580 USA/Europe 120 5600 USA/Europe 124 5620 USA/Europe 128 5640 USA/Europe 132 5660 USA/Europe 136 5680 USA/Europe 140 5700 USA/Europe 149 5745 USA 153 5765 USA 157 5785 USA 161 5805 USA 165 5825 USA

TABLE 6 2.4 GHz, 20 MHz channel BW, 192 Mbps max bit rate TX ST Anten- Code Code Rate nas Rate Modulation Rate NBPSC NCBPS NDBPS 12 2 1 BPSK 0.5 1 48 24 24 2 1 QPSK 0.5 2 96 48 48 2 1 16-QAM 0.5 4 192 96 96 2 1 64-QAM 0.666 6 288 192 108 2 1 64-QAM 0.75 6 288 216 18 3 1 BPSK 0.5 1 48 24 36 3 1 QPSK 0.5 2 96 48 72 3 1 16-QAM 0.5 4 192 96 144 3 1 64-QAM 0.666 6 288 192 162 3 1 64-QAM 0.75 6 288 216 24 4 1 BPSK 0.5 1 48 24 48 4 1 QPSK 0.5 2 96 48 96 4 1 16-QAM 0.5 4 192 96 192 4 1 64-QAM 0.666 6 288 192 216 4 1 64-QAM 0.75 6 288 216

TABLE 7 Channelization for Table 6 Channel Frequency (MHz) 1 2412 2 2417 3 2422 4 2427 5 2432 6 2437 7 2442 8 2447 9 2452 10 2457 11 2462 12 2467

TABLE 8 5 GHz, 20 MHz channel BW, 192 Mbps max bit rate TX ST Anten- Code Code Rate nas Rate Modulation Rate NBPSC NCBPS NDBPS 12 2 1 BPSK 0.5 1 48 24 24 2 1 QPSK 0.5 2 96 48 48 2 1 16-QAM 0.5 4 192 96 96 2 1 64-QAM 0.666 6 288 192 108 2 1 64-QAM 0.75 6 288 216 18 3 1 BPSK 0.5 1 48 24 36 3 1 QPSK 0.5 2 96 48 72 3 1 16-QAM 0.5 4 192 96 144 3 1 64-QAM 0.666 6 288 192 162 3 1 64-QAM 0.75 6 288 216 24 4 1 BPSK 0.5 1 48 24 48 4 1 QPSK 0.5 2 96 48 96 4 1 16-QAM 0.5 4 192 96 192 4 1 64-QAM 0.666 6 288 192 216 4 1 64-QAM 0.75 6 288 216

TABLE 9 channelization for Table 8 Frequency Frequency Channel (MHz) Country Channel (MHz) Country 240 4920 Japan 244 4940 Japan 248 4960 Japan 252 4980 Japan 8 5040 Japan 12 5060 Japan 16 5080 Japan 36 5180 USA/Europe 34 5170 Japan 40 5200 USA/Europe 38 5190 Japan 44 5220 USA/Europe 42 5210 Japan 48 5240 USA/Europe 46 5230 Japan 52 5260 USA/Europe 56 5280 USA/Europe 60 5300 USA/Europe 64 5320 USA/Europe 100 5500 USA/Europe 104 5520 USA/Europe 108 5540 USA/Europe 112 5560 USA/Europe 116 5580 USA/Europe 120 5600 USA/Europe 124 5620 USA/Europe 128 5640 USA/Europe 132 5660 USA/Europe 136 5680 USA/Europe 140 5700 USA/Europe 149 5745 USA 153 5765 USA 157 5785 USA 161 5805 USA 165 5825 USA

TABLE 10 5 GHz, with 40 MHz channels and max bit rate of 486 Mbps TX ST Code Code Rate Antennas Rate Modulation Rate NBPSC 13.5 Mbps 1 1 BPSK 0.5 1 27 Mbps 1 1 QPSK 0.5 2 54 Mbps 1 1 16-QAM 0.5 4 108 Mbps 1 1 64-QAM 0.666 6 121.5 Mbps 1 1 64-QAM 0.75 6 27 Mbps 2 1 BPSK 0.5 1 54 Mbps 2 1 QPSK 0.5 2 108 Mbps 2 1 16-QAM 0.5 4 216 Mbps 2 1 64-QAM 0.666 6 243 Mbps 2 1 64-QAM 0.75 6 40.5 Mbps 3 1 BPSK 0.5 1 81 Mbps 3 1 QPSK 0.5 2 162 Mbps 3 1 16-QAM 0.5 4 324 Mbps 3 1 64-QAM 0.666 6 365.5 Mbps 3 1 64-QAM 0.75 6 54 Mbps 4 1 BPSK 0.5 1 108 Mbps 4 1 QPSK 0.5 2 216 Mbps 4 1 16-QAM 0.5 4 432 Mbps 4 1 64-QAM 0.666 6 486 Mbps 4 1 64-QAM 0.75 6

TABLE 11 Power Spectral Density (PSD) mask for Table 10 PSD Mask 2 Frequency Offset dBr −19 MHz to 19 MHz 0 +/−21 MHz −20 +/−30 MHz −28 +/−40 MHz and −50 greater

TABLE 12 Channelization for Table 10 Frequency Frequency Channel (MHz) Country Channel (MHz) County 242 4930 Japan 250 4970 Japan 12 5060 Japan 38 5190 USA/Europe 36 5180 Japan 46 5230 USA/Europe 44 5520 Japan 54 5270 USA/Europe 62 5310 USA/Europe 102 5510 USA/Europe 110 5550 USA/Europe 118 5590 USA/Europe 126 5630 USA/Europe 134 5670 USA/Europe 151 5755 USA 159 5795 USA 

1. A method for generating a preamble of a frame for a multiple input multiple output (MIMO) wireless communication, the method comprises: for each transmit antenna of the MIMO wireless communication, generating a carrier detect field, wherein, from transmit antenna to transmit antenna; for a first grouping of the transmit antennas of the MIMO wireless communication: generating a first guard interval following the carrier detect field; generating at least one channel sounding field with respect to each transmit antennas of the first grouping, wherein the at least one channel sounding field follows the first guard interval; and for each transmit antenna of the first grouping, applying a cyclic shift prior to transmission; and when the MIMO wireless communication includes more than the first grouping of the transmit antennas, for another grouping of the transmit antennas: generating at least one other channel sounding field for each transmit antenna of the another grouping, wherein, from transmit antenna to transmit antenna in the another grouping, the at least one other channel sounding field follows the at least one channel sounding field; and generating the first guard interval prior to the at least one other channel sounding field; and for each transmit antenna of the another grouping, applying another cyclic shift prior to transmission of the another grouping.
 2. The method of claim 1 further comprises, for each transmit antenna of the first grouping of the transmit antennas of the MIMO wireless communication: generating a second guard interval following the at least one channel sounding field; and generating a signal field following the second guard interval.
 3. The method of claim 2 further comprises, for each transmit antenna of the another grouping of the transmit antennas: generating a third guard interval preceding the at least one other channel sounding, wherein the first and third guard intervals are greater in duration than the second guard interval.
 4. The method of claim 1, wherein the generating the carrier detect field comprises: generating a short training sequence in accordance with a legacy protocol is based on a number of the transmit antennas and duration of the short training sequence.
 5. The method of claim 4 further comprises, when the number of transmit antennas is three: for the first grouping of the transmit antennas of the MIMO wireless communication, generating a first and second long training sequence in accordance with the legacy protocol as at least one channel sounding field, wherein the first grouping includes two of the three transmit antennas; and generating a third long training sequence in accordance with the legacy protocol as the at least one other channel sounding field for the another grouping of the transmit antennas, wherein the another grouping includes a third of the three transmit antennas.
 6. The method of claim 4 further comprises, when the number of transmit antennas is four: for the first grouping of the transmit antennas of the MIMO wireless communication, generating a first and second long training sequence in accordance with the legacy protocol as at least one channel sounding field, wherein the first grouping includes two of the four transmit antennas; and generating third and fourth long training sequences in accordance with the legacy protocol as at least one other channel sounding field for the another grouping of the transmit antennas, wherein the another grouping includes another two of the four transmit antennas.
 7. The method of claim 1 further comprises for each of the transmit antennas of the MIMO wireless communication: generating another guard interval following the at least one other channel sounding field; and generating a second signal field following the another guard interval.
 8. A method for generating a legacy compatible preamble of a frame for a multiple input multiple output (MIMO) wireless communication, the method comprises: for each transmit antenna of a plurality of transmit antennas for the MIMO wireless communication, generating a carrier detect field, wherein, from transmit antenna to transmit antenna; for a first transmit antenna of the plurality of transmit antennas: generating a first guard interval following the carrier detect field; generating a first channel sounding field following the first guard interval; generating a second channel sounding field following the first channel sounding field; and applying a cyclic shift prior to transmission via the first transmit antenna of the plurality of transmit antennas; and for each transmit antenna of a first grouping of remaining transmit antennas of the plurality of transmit antennas: generating a third channel sounding field; generating a fourth channel sounding field following the third channel sounding field; generating a second guard interval preceding the third channel sounding field; and applying a cyclic shift prior to transmission via the each transmit antenna of the first grouping of the remaining transmit antennas.
 9. The method of claim 8, wherein when the plurality of transmit antennas includes four transmit antennas: for a fourth transmit antenna of the plurality of transmit antennas: generating a fifth channel sounding field; generating a sixth channel sounding field following the fifth channel sounding field; and generating a third guard interval preceding the fifth channel sounding field.
 10. The method of claim 9 further comprises for each of the plurality of transmit antennas: generating another guard interval following the sixth channel sounding field; and generating a signal field following the second guard interval.
 11. The method of claim 8 further comprises, for the first transmit antenna: generating another guard interval following the second channel sounding field; and generating a signal field following the second guard interval.
 12. The method of claim 8, wherein the generating the carrier detect field comprises: generating a short training sequence in accordance with a legacy protocol is based on a number of the transmit antennas and duration of the short training sequence.
 13. The method of claim 8 further comprises for each of the transmit antennas of the MIMO wireless communication: generating another guard interval following the fourth channel sounding field; and generating a second signal field following the another guard interval.
 14. A radio frequency (RF) transmitter comprises: a baseband processing module that produces outbound symbol streams from outbound data; and a transmitter section that produces outbound RF signals from the outbound symbol streams, wherein the baseband processing module is operable to: for each transmit antenna of the transmitter section, generate a carrier detect field, wherein, from transmit antenna to transmit antenna for a first grouping of the transmit antennas of the transmitter section: generate a first guard interval following the carrier detect field; generate at least one channel sounding field, wherein, from transmit antenna to transmit antenna in the first grouping, wherein the at least one channel sounding field follows the first guard interval; and for each transmit antenna of the first grouping, applying a cyclic shift prior to transmission; and when the transmitter section includes more than the first grouping of the transmit antennas, for another grouping of the transmit antennas: generate at least one other channel sounding field, wherein, from transmit antenna to transmit antenna in the another grouping, wherein the at least one other channel sounding field follows the at least one channel sounding field; and generate the first guard interval prior to the at least one other channel sounding field; and for each transmit antenna of the another grouping, applying another cyclic shift prior to transmission of the another grouping.
 15. The RF transmitter of claim 14, wherein the baseband processing module is further operable to, for each antenna of the first grouping of the transmit antennas of the transmitter section: generate a second guard interval following the at least one channel sounding field; and generate a signal field following the second guard interval.
 16. The RF transmitter of claim 15, wherein the baseband processing module is further operable to, for each antenna of the another grouping of the transmit antennas: generate a third guard interval preceding the at least one other channel sounding, wherein the first and third guard intervals are greater in duration than the second guard interval.
 17. The RF transmitter of claim 14, wherein the baseband processing module is further operable to generate the carrier detect field by: generating a short training sequence in accordance with a legacy protocol based on a number of the transmit antennas and duration of the short training sequence.
 18. The RF transmitter of claim 17, wherein the baseband processing module is further operable to, when the number of transmit antennas is three: for the first grouping of the transmit antennas of the transmitter section, generate a first and second long training sequence in accordance with the legacy protocol as at least one channel sounding field, wherein the first grouping includes two of the three transmit antennas; and generate a third long training sequence in accordance with the legacy protocol as the at least one other channel sounding field for the another grouping of the transmit antennas, wherein the another grouping includes a third of the three transmit antennas.
 19. The RF transmitter of claim 17, wherein the baseband processing module is further operable to, when the number of transmit antennas is four: for the first grouping of the transmit antennas of the transmitter section, generate a first and second long training sequence in accordance with the legacy protocol as at least one channel sounding field, wherein the first grouping includes two of the four transmit antennas; and generate third and fourth long training sequences in accordance with the legacy protocol as at least one other channel sounding field for the another grouping of the transmit antennas, wherein the another grouping includes another two of the four transmit antennas. 